Closed-loop material transport system, including an in-circuit pulverizer



Feb..24,194's. up. SHERB'AN f2,436,4s1

CLOSEDLLOOI MATERIAL TRANSPORT SYSTEM, INCLUDING AN IN-CIRCUITPULVERIZER Filed Dec. 11. 1943 2 sheets-sheet 1 I v (Je 724 @L Fi 1 2620 I:Q2 m4. o /v 106 `68 38 INVENToR.

A ITORNH Y Feb. 24, 1948. D. v. sHEBAN 2,436,487

CLOSED-LOOP MATERIAL TRANSPORT SYSTEM, INCLUDING. AN IAN-CIRCUITPULVERIZER med nec. 11, 194s 2 Sheets-Sheet Patented Feb. 24, 1948 TEM,INCLUDING AN VERIZER IN -CIRCUIT PUL- Daniel V. Sherban, Keyport, N. J.,asslgnor to The Babcock & Wilcox Company, Rockleigh, N. J., acorporation of New Jersey Application December 11, 1943, Serial No.513,842

The invention herein disclosed relates to a pulverizing apparatusespecially adapted for use in a system wherein pulverized products aretransported from the apparatusby means oi a current of air or othersuitable gaseous carrier medium, and varying proportions of suchproducts are returned to the apparatus for recycling. The apparatus andsystem will be found suitable for use with materials of variouscomposition including, for example, such solids as coal, mineral ores,cement clinker, or other solids of similar physical characteristics.

'I'he invention may be usefully applied-in a pulverized fuel ring systemwherein pulverized coal is discharged from the pulverizer or mill in astream of carrier air, and the resulting fluent mixture delivered to aburner, or to a number of burners, with any surplus quantity of themixture being returned to the mill to provide continuous circulation. Insuch a system, provision is made for feeding raw coal vto the pulverizerat rates sucent to replace the amounts taken by the burner or burners,and for supplying fresh or make-up air to the pulverizer at ratessumcient to maintain a current i air therethrough at all loads whileproviding an output mixture having the particular fuel-to-air ratiodesired for any given load.

In certain types of pulverizers wherein grinding elements are relativelyrotatable about a vertical axis, the coal and make-up air areconveniently supplied to the pulverizing zone from opposite sides, thatis, the raw coal being fed from the upper side for discharge by gravityinto the zone, and the fresh air being supplied from the under sideforadmission to the zone in an annular stream. Since the fuel-airmixture is iluent in character, any surplus of the mixture to bereturned to the mill may be mingled with the incoming supply oi make-upair, prior to admis- Y 1l Claims'. (Cl. 241-48) sion of the air to thegrinding zone, thereby producing a carrier medium of modied densitywhich may be admitted to the grinding zone through the passage orpassages normally provided for the fresh air alone.

Under normal operating conditions, the coal and air are supplied to thepulverizer in such proportions that the resulting output mixturecontains a smaller quantity of -air than is necessary for completecombustion; thus, the mixture with its normal content of primary air maybe transported from the pulverizer without risk of pre- `maturecombustion or explosion, and the required amount of secondary airvmay beadded combustion of the entrained coal'particles.

at the burners to provide a suitably combustible mixture.

When a surplus of the mixture is returned to l the pulverizer, as in thecirculating system herein disclosed, the fuel and air content'. of thereturning mixture remains essentially the same as when originallydischarged from the pulverizer,

tained throughout the return conduit system to prevent any appreciablequantity of pulverized coal from settling out of the returning stream.When the return mixture and the make-up or primary air are combined forflow through the grinding zone,l the proportion of air in the resultingmixture is appreciably higher than in the returning fuel air mixture,thereby tending to provide an atmosphere capable of supportinlg t isconsidered important therefore to avoid any condition which might leadto ignition of such a mixture to cause a possible explosion, eitherthrough the coking of pulverized coal accumulations in or adjacent thezone of mixing; or as a result of hot coke particles being carried intothe mixing zone and allowed to accumulate therein, When a heated supplyof primary air is employed, the hazard of the mixture becom-` ingignited is somewhat increased, due to a cer-A tain amount of .heat beingretainedin the returning coal-air mixture which would tend to promotecoke formation.

It is a purpose of the invention therefore to maintain the iluid flowpassages leading to the grinding zone clear of all coal or'cokeaccumulations, and to cause the make-up air and the returning coal andair to be vmixed in a zone where-there is the least tendency for coalorcoke to collect.

An additional object is to maintain velocities of iluid flow into themixing zone high enough tokeep the adjoining passages clear of anypulverized coal or coke that mightv tend to settle therein.

Another object is to cause the respective streams to enter the mixingzone in such directions and at such velocities as to promote thoroughmingling of the streams throughout the zone.

A further Objectis to provide a mixing zone having an outlet direct tothe grinding zone or adjoining region where the issuing stream willpickup additional coal particles, thereby increasing the proportion ofcoal to air in the mixture and providing a relatively non-explosivemixture for ilow through and from the pulverizer,

amaca? 3 the area of now from the mixing zone into the grinding zone tobe small enough to maintain now velocities at least as high as thevelocities' prevailing within the mixing zone, and higher than the rateof flame propagation for the fueland-air mixture in transit at thatlocation- Among other objects, it is proposed to maintain the passagesleading to and from the mixing zone clear of oversize particles or otherforeign materials which might tend to obstruct the flow of air andpulverlzed coal.

More specific objects include the admission of coal-free air andcoal-laden air to the pulverizer through concentrically arranged inletareas; the mixing of both bodies of air in an'annular zone closelyadjacent the grinding zone; and the admission of the coal-laden airthrough an opening v arranged out of the path of solids falling from thegrinding zone.-

The foregoing objects and others not specincally mentioned are morefully set forth in the description to follow, together with variousadvantageous features of construction as illustrated in the accompanyingdrawings. in which:

Fig. 1 is a layout, in plan, of a pulverlzed coal circulating systemembodying apparatus of my invention;

Fig. 2 is an elevational view, partly in section, of the pulverizerincluded in the system of Fig. 1;

Fig. 3 is a plan section of the pulverizer, taken along line 3-3 of Fig.2;

Fig. 4 is an enlarged fragment of Fig. 2;

Fig. 5 is an enlarged fragmentary section, similar to Fig. 4, showing amodication.

The system according to Fig. 1 of the drawings, includes an air sweptpulverizer I0 arranged to supply pulverized coal and primary air toburners I2 and I4 associated with a form of metallurgical furnace I6.here indicated as a billet heating furnace, although as will beunderstood. other types of furnaces may be employed and, if desired, theburners arranged for ring separate furnaces.

The pulverizer I0 is shown as being located adjacent the charging end I8of the furnace I6 and its output ofv pulverlzed coal and primary air isdischarged through pipe to the inlet of an exhauster fan 22 from whichthe mixture is delivered to a main distributor conduit 24 at its inletend 26, the opposite end or return length 28 of the conduit beingconnected to the air inlet side of the pulverizer to form a closedcircuit or loop as will be explained more in detail hereinafter. Thepulverizer and fan are conveniently operated by a single motor 30.

or group of burners, that it may be desired to maintain in operation;the burners I2 along one side of the furnace being supplied throughburner lines 32 leading from the conduit 24, the larger burners I4 atthe discharging end of the furnace remote from the location of thepulverizer being supplied through burner lines 34, and the remainingside burners I2 through additional burner lines 32. Suitable valves, notshown, may be installed in each of the burner lines 32 and 34 topositively cut of the supply of fuel and primary air to any burner notin operation, and to regulate the supply of fuel to the various burnersduring operation. Any surplus quantity of the total pulverizer outputabove that diverted to the burner or burners in operation is returned tothe inlet side of the pulverizer I0 for recycling in view of the loopedarrangement of the conduit 24 which provides a closed circulatorysystem. A secondary supply of air may be admitted to the burners or tothe furnace or furnaces for complete coinbustion of the fuel, but'thedetailsof such secondary supply are not included in the presentinvention, and further disclosure is therefore considered unnecessary.

The references to coal as the material being pulverized, and to air asthe carrier medium, are not to be taken literally. but are to beinterpreted as embracing other solids, combustible or otherwise, andother gaseous media, capable of adaptation to the system described. In abroad sense, also, the burners I2 and I4 become selected points ofdelivery or use, for example, bins or other containers, irrespective ofwhether the material transported is a fuel or is a material ofnoncombustible character.

Referring to Fig. 2, the pulverizer I0, is by way of example, of a knownball-mill type having its grinding zone located in the lower portion ofan enclosing casing or housing 36 generally circular in cross-sectionabout a vertical axis. The grinding elements include a circular seriesof grinding balls 38 which cooperate with upper and lower grinding rings40 and 42 'respectively to reduce the coal to the desired degree ofneness; the raw coal being delivered to the pulverizing chamber 44 abovethe level of the grinding rings by means of a known type of motor drivenfeeder 46 mounted on the pulverizer casing 36.

In this form of pulverizer, the lower grinding ring 42 is maintainedstationary, being mounted on an annular support 48 integral with thebase plate 50 which forms the bottom wall of the casing or housing 36.The upper grinding ring 40, concentric with the lower grinding ring 42,is rotated about its central vertical axis to cause the balls 3B to rollrelative to both grinding rings; the upper grinding ring 40 beingdrivenby motor 30 operating through pinion shaft 52 and suitable gearingwithin housing 54 to rotate the drive member 56 and drive ring 58.Grinding pressure between the balls and rings may be resiliently andadjustably maintained by means Well known in the art.

A conical wall 60 surrounding the lower grinding ring 42 and flaringupwardly toward the casing 36 serves to guide the incoming raw coal intothe zone of action of the balls 38; the wall 60 extending upwardly fromthe annular support 48 to define an annular compartment 62 in whichfresh make-up' air is admitted through conduit 64 and from which suchair is discharged inwardly through a series of circumferentially spacedports 66 in the annular support 48. The air admitted through conduit 64may be heated or un- `heated, as desired, and the conduit fitted withthe usual regulating damper or dampers, as desired.

A downwardly flaring cup-like member 58, rotatable with the drive member56 and constituting in effect an integral extension thereof, terminatesin a cylindrical outer surface portion 16 adjacent its lower edge at alevel corresponding to the reduced inner edge portion 12 of the lowergrinding ring 42, thereby forming a relatively narrow annular passage orthroat 14 through which carrier air is admitted to the grinding zoneabove. The coal is fed to the region exteriorly of thecircle of balls 38and as the coal becomes pulverlzed, the particles are swept upwardly bythe stream of carrier fluid admitted to the grind s in the regionlnteriorly oi' the circle and discharged laterally through -a'circumferential series of ports 'i6 in the drive ring 68. The finerparticles continue upwardly through the cham,- ber M and are dischargedfrom the pulverizer through the outlet 20, while the coarser particlesdropout ofthe current and are returned to the pulverizing zone forfurther reduction.

The extension member 68, as shown. comprises an assembly of platemembers including, for example, a downwardly flaring conical side ywallplate 78, a cylindrical upper side wall plate 00, and a circular top orclosure plate 82, A conical plate 80 arrangedinwardly of the conicalplate I8 and diverging downwardly therefrom provides an effectivethickness for the lower side wall portion of. member 68 of graduallyincreasing cross section toward the bottom a pipe 06 formed as a ringbeing positioned between the downwardly diverging plates 'i8 and 04 andbeing welded to their lower edges to afford rigidity to the assembly andto provide a rounded bottom edge or rim 88. .A downwardly flaringconical plate 90 having an upturned circumferential lip portion 92 ispositioned below the rim 80, being secured to the inner plate 84, forexample, by means of circumferentially spaced ribs 90.

kThemember 68 is provided exte'riorly with a series of circumferentiallyspacedv vanes 05 adjacent its lower edge, such varies extendingdownwardly to provide portions within the throat 'i0 and serving tomaintain the throat area clear of coarse, heavy particles of materialthat might interfere with free fluid flow therethrough; the

'below the throat 1I where it is mingled with fluid entering from thepassage |20 formed betweenA the rim 88 and plate 90,01 `the rotatingmember 68, the mixture of the two bodies of fluid then passing upwardlythrough the4 throat 'I4 and grinding zone above. f

The stream of coal and air returned to the pulverizer by means ofconduit sections 86 and |00 is caused to ow upwardly to enter thev space|02 centrally of the rotating member 66, whereupon the direction of itsflow is reversed and the stream converted to one of annular formdirected downwardly through the passage |22 between the conical sidewall portions of the rotating member 68 and the stationary member |06.The downward flow of the returned fuel and air is continued through theannular passage I 20 where the stream is deflected upwardly b'y the lip92 into -impingement with the upwardly flowing stream of make-up airwithin the mixing zone H8. 'i

lIn this arrangement of pulverizer. the central inlet |04 for thereturning fuel-and-air mixture is above the level of the throat 14 andtherefore out of the path of any material such as pyrites or othercoarse, heavy particles that might fall through the throat and interferewith normal uid flow conditions in the fluid circulation system. Such anarrangement is particularly desirable in circulation systems wherein ameasure high velocity of flow throughout, the velocity of posed conduitsection |00 extends from the base plate opening 98 into the upperportion of the space |02 interiorly of the member 68, the section |00terminating in an open upper end |04 of circular cross sectionconstituting the area of ad-I Vslightly less than the inner edge of theplate 90 to provide an annular clearance space ofsuitable width forrelative rotation.

In the operation-of the system described, .the supply of make-up airadmitted to the pulverizerthrough conduit 6l is distributed throughoutthe annular compartment 62 from which it is directed through thecircumferentially spaced ports 66 to the annular space III disposedbetween the ring support 48 and the conical baille memberv |06,

the upper wall of each port 66 being inclined downwardly at its innerend, as at ||6, to afford entrance to thev space ||4 at a, level belowthe outer edge of plate 90. The air then passes up- Wardly to theannular zone ||8 immediately vdischarge 'through the outlet passage |20being sufficient to effect thorough mingling of the coalladen air withthe 'coal-free air within the annular zone H8. The two bodies of air ofdifferent densities thus delivered to the zone ||8 are combined to forma fluid mixture of modified density in which the solid particles aresubstantially uniformly distributed throughout and in which undercertain conditions the air content may be sulcient to provide anexplosive mixture. The hazard'of a fire or an explosion of the mixtureis substantially eliminated however by effecting the mixture of the twobodies in a zone of high 'fluid flow velocities where there is the leasttendency for coke to collect, and where velocities are preferably higherthan the rate of ilame propagation forl the -fuel and air mixture intransit; in the embodiment disclosed, the mixing being eiected in anannular zone of restricted dimensions closely adjacent the pulverizerthroat 14 where velocities are maximum, in practicea suitable mixinglevel being at a distance below the throat 'I4 of approximately twotimes the width of the throat or corresponding passage where maximumvelocities are initiated, such velocities being maintained into thegrinding zone or adjacent region where additional fuel particles areimmediately picked up to restore the normal fuel content and therebyrender the mixture relatively non-explosive for discharge from thepulverizer. The downward. flow of fluid at high velocity through thepassages |22 and |20 also `serves to overcome any tendency for coal towork up toward and into the inlet opening |04.

In Fig. 5, showing a modicatiomparts correspending to those included inFig, 4 are identified by the same reference characters. In this embodiment of the invention, the inner conical wallv the cone |24 andattached thereto, may be em ployed to further improve distribution, andto assist in overcoming a part of the entrance pressure drop. Blades|28, circumferentially spaced and secured to the inner side wall portion84 of member 68, tend to further induce air flow and prevent coal fromworking up toward the inlet |04, particularly when the amount of coal inthe mill is above normal; the blades |23 being pitched forwardly andhaving their free edges |30 closely adjacent and substantially parallelto the outer surface of the stationary cone |06 whose slope, in thisform, is continuous from the rim of the inlet opening |04 to the baseplate 50'. A manifold |32, in the form of a ring and provided withopenings |34 about its circumference, may be suitably connected to asource of high pressure air orother fluid for the purpose of clearingthe space ||4 of pyrites or other debris that might have accumulated,the openings |34 registering with corresponding openings in the cone |06to provide jets directed toward the ports 66 so that the obstructingmaterial may he dislodged and forced into the chamber 62 from which itmay be readily removed. l

I claim:

l. In a pulverizer having grinding elements in the lower portion of anenclosing housing, said housing having an outlet leading fromits upperportion, said elements comprising a member formed with a grindingsurface arranged annularly about'a vertical axis and a circle ofgrinding members arranged coaxially with said surface and adapted tocooperate therewith for pulverizing material fed into said housing at alocation above said grinding elements, means forming an annular throatconcentric with fand adjacent a circumference of said annular grindingsurface, means for causing a stream of carrier air to flow upwardlythrough said throat for transporting pulverized material particles t'oand through said outlet, means for admitting a portion of said carl rierair to a zone ,within said housing displaced inwardly and upwardly fromthe entrance .to said annular throat, means for directing said portionto a surrounding annular zone below and adjacent said throat, means forseparately admitting another portion-of said carrier air to said annularzone, means' for causing said portions to become mingled within saidannular zone, and means for directing 'said mingled portions upwardlythrough said throat to provide said stream of carrier air.

2. I an air swept pulverizer adapted for inclusion in a circulationsystem such as described, means forming a grinding zone in the lowerportion of the pulverizer housing, said means including a ring memberhaving an annular grinding surface formed about a vertical axis andspaced above the inside bottom wall of said housing, ymeans including adownwardly expanding conical baille for defining an` annular throatadjacent the inner circumference of said grinding member, said bailleterminating in a. lower.

rim portion forming the inner circumferential boundary of said throat,means for admitting material-laden air to said pulverlzer comprising aconduit arranged centrally of said conical bale and extending upwardlytherein beyond the level of said lower rim portion and throat, a conicalbaille coaxial with said conduit and sloping downwardly therefrom to thebase of said housing to define an annular space below and adjacent saidthroat, said baiiles being spaced throughout to form an annular passagefor conducting material-laden air from said conduit to said annularspace, a support for said ring member formed with a series ofcircumferentially spaced ports for directing material-free air to saidannular space, means for causing said streams of air to be mixed withinsaid annular space at a location closely adjacent said throat, and meansfor causing the resulting mixture to ow upwardly through said throatinto said grinding zone.

3. In an air swept pulverizer adapted for in- .clusion in a circulationsystem such as described,

upper and lower grinding rings together with an intermediate circle ofrollable grinding elements cooperating therewith to form an annulargrinding zone within the lower portion of the pulverizer housing, meansincluding a downwardly expanding conical baffle for defining an annularthroat adjacent the inner circumference of said lower grinding ring,said baiile terminating in a lower rim portion forming the innercircumferential boundary of said throat, means for admittingmaterial-laden air to said pulverizer comprising a conduit arrangedcentrally of said conical baffle and extending upwardly therein beyondythe level of said lower rim portion and throat, a conical baillecoaxial with said conduit and sloping downwardly from the upper endthereof to the base of said housing to define an annular space below andadjacent said throat, said conical bailes being spaced throughout toform an annular passage for conducting material-laden air from saidconduit to said annular space, said first named battle having a conicalinner surface portion diverging downwardly from a conical outer'surfaceportion to provide an effective wall thickness progressively greatertowards its lower edge thereby progressively decreasing the distancebetween said baille's at increasing diameters to provide a relativelyhigh velocity of discharge of materialladen air into said annular space,means for separately directing material-free air into said annular spaceand causing said air Ato become mingled with said material-laden airwithin said space, and means for inducing upward flow of the resultingmaterial and air mixture through said throat.

4. In an air swept pulverizer adapted for inclusion in a circulatingsystem such as described, upper and lower grinding rings together withan intermediate circle of rollable grinding elements cooperatingtherewith to form an annular grinding zone within the lower portion ofthe pulverizer housing, means for admitting materialladen airto saidpulverizer comprising a conduit arranged centrally of said grinding zoneand terminating in an open upper end at approximately the level of saidcircle of grinding elements, means for directing said material-laden airfrom the upper end of said conduit to an annular mixing zone below andadjacent said grinding zone, said last named means comprising adownwardly flaring conical baille disposed over the upper open end ofsaid conduit and terminating in a lower rim portion defining an annularthroat adjacent the inner circumference of said lower grinding ring,said baille forming the outer wall oi' an y resulting modified mixtureto flow upwardly` through said throat.

5. In an air swept pulverizer adapted for inclusion in a circulationsystem such as described, upper and lower grinding rings together withan intermediate circle ofvrollable grinding elements cooperatingtherewith to form an annular grinding zone within the lower portion ofthe pulverizer housing, means for admitting material-laden air to'saidpulverizer comprising a conduit arranged centrally of said grinding zoneand terminating in an open upper end at approximately the level of saidcircle of grinding elements, means for directing said material-laden airfrom the upper end of said conduit to an annular mixing zone below andadjacent said grinding zone, said last named means comprising. adownwardly iiaring conical baille disposed over the upper open end ofsaid conduit and terminating in a lower rirn portion defining an`annular throat adjacent the inner circumference of said lower grindingring, saidy baille including a top portion formed as a cone having' itsapex pointed downwardly toward the open end `of said conduit, means for`mixing an additional supply of air with said material-laden air in saidmixing zone, and means for causing the resulting modified mixture tofiow upwardly through said throat.

6. In a closed circulating system of the type described, an air. sweptpulverizer having a normal output of pulverized combustible material andair in a ratio providing a substantially nonexplosive mixture, saidpulverizer having a grinding zone Within an enclosing housing having anoutlet at one side of said zone through which said mixture isdischarged, means defining said grinding zone comprising a memberproviding an annular grinding surface having an inlet and an outletmarginal circumference, means at the side toward said outlet feedingcombustible material to said grinding zone adjacent said inletcircumference, means for returning to said pulverizer a portion of saidoutput mixture composed of pulverized combustible material and air insubstantially the aforesaid ratio, said last named means being arrangedto direct said portion `to an annular mixing space disposed adjacent theside ofy said grinding' zone remote from said outlet, said mixing spaceterminating in an4 annular outlet passage of restricted flow areaadjacent said outlet circumference, means for supplying material-freecarrier air to said pulverizer arranged to direct said air into saidmixing space thereby combining said material-free air with thecombustible-material-laden air returned from said outlet and producing amodified mixture of potential explosive character, means for causingsaidmodi-l fied mixture to flow through said outlet passage fortransporting pulverized combustible material from said grinding zone toprovide said normal output mixture, and means for maintaining thevelocity of flow of said modified mixture within and from said mixingspace higher than the rate of flame propagation of said mixture asproduced in said space.

'1. In a closed circulating system of the type described, an air sweptpulverizer having a nor.

mal output of pulverizedcombustlble material and air in a ratioproviding a substantially noning zone adjacent said outer circumference,

means for returning to said pulverizer a portion of said output mixturecomposed of pulverized combustible material and air in substantially theaforesaid ratio, said last named means being arranged Ito direct saidportion to an annular mixing space disposed adjacent the lower side ofsaid grinding zone, said mixing space terminating in an annular outletpassage of restricted flow area adjacent said inner circumference, meansfor supplying material-free carrier lair to said pulverizer arranged todirect said air into said mixing space thereby combining saidmaterial-free air with the combustible-materialladen air returned fromsaid outlet and producing a modified mixture of potential explosivecharacter, means for causing said modified mixture to flow through saidoutlet passage for transporting pulverized combustible material fromsaid grinding zone to provide said normal output mixture, and means formaintaining the velocity of ow of said modified mixture within and fromsaid mixing space higher than the rate of flame propagation of saidmixture as produced in said space.

'8. In a pulverizer adapted for inclusion in a circulating system suchas described, said pulverizer having a grinding zone of annularformation about a vertical axis, said housing having an outlet'therefrom at the upper side of' said grinding zone, means defining saidgrinding zone comprising a ring member concentric with respect to saidaxis and providing an annular grinding surface between an inlet and anout- -let marginal circumference each disposed at a different radialdistance from said axis. means feeding coal to the upper side of saidgrinding zone adjacent said inlet circumference, means forming anannular throat concentric with and adjacent said outlet circumference,means for causing a stream of carrier air to flow upwardly through saidthroat for transporting pulverized coal to and through said outlet,means for admitting a portion of said carrier air to a zone within saidhousing displaced radially and upwardly from the entrance to saidannular throat,

means for directing said portion to an annular mixing zone below andadjacent said throat, means for combining an additional carrier airportion with said first named portion within said mixing zone, saidcarrier air portions consisting of coal-free and coal-laden airrespectively, and means for effecting iiow of said respective carrierair portions into said mixing zone and of said combined portions withinand from said zone at velocities high enough to maintain the associatedow passages clear of coke accumulations.

9. In van air swept pulverizer adapted for inclusion in a closedcirculating system of the type disclosed, said pulverizer havinggrinding elements in the lower Aportion ofan enclosing housing, saidhousing having an outlet leading from its upper portion, said elementscomprising a member formed with a grinding surface arranged annularlyabout a vertical axis between an inner and an outer marginalcircumference each at a different radial distance from said axis', meansdefining an annular throat adjacent said inner circumference, meansdeiining an annular space below and adjoining said throat, means fordirecting separate bodies of air into said space in streams distributedsubstantially throughout its circumference,` one of said bodies of aircomprising a` material-laden portion of the total pulverizer output andone substantially clean air from a separate source, means for causingone of said bodies of air to flow outwardly from said axis to enter saidspace, means for causing the other of said bodies to flow inwardlytoward said axis to enter said space to eiIect a mixture with saidoppositely entering body of air, and fan means causing upward flow ofsaid mixture into and through said throat.

10. In a pulverizer having grinding elements in the lower portion of anenclosing housing, said housing having an outlet leading from its upperportion, said elements including a member formed with a grindingsurfacearranged annularly about a vertical axis between'a material inletcircumference and a material outlet circumference disposed at dinerentradial spacings from said axis, means forming an annular throat adjacentsaid outlet circumference means for causing air to flow through saidthroat for transporting particles of pulverized material to and throughsaid outlet, means for admltting said air to said pulverzeiin separatestreams of which one stream is composed of relatively clean air andanother is composed of air in which pulverized material particles aresuspended, said streams being admitted to the interior of said housingin concentric relation relative to said vertical axis, means deiinlng anannular space in the region below and adjacent said throat, means forcausing said streams to become mingled in said annular space, and meansfor directing the resulting mixture upwardly through said throat.

11. In an air swept pulverlzer adapted for inrounded lower rim portionforming the inner circumferential boundary of said throat, means forsupplying fluid streams of different densities to said pulverlzer forsubsequent mingling ,and flow through said throat, means for admittingone of said streams to the interior of said pulverizer'comprising a pipearranged centrally of said bell-shaped member and extending upwardlytherein beyondthe level of said lower rim portion and throat, means foradmitting the other of said streams to the interior 'of said pulverizerannularly of said upwardly extending pipe, means for reversing the nowof said first named stream to form an annular stream tiowing downwardlyadjacent the interior wall of said bellshaped member toward an annularzone belowand adjacent said throat, a deiiector ring surrounding saidpipe having an upper surface portion formed to deflect said downwardlyflowing stream into mixing relation with the other of said streams insaid zone, and means for causing the resulting mixture to now upwardlythrough said throat.

DANIEL V. SHERBAN.

REFERENCES CITED The following references are of record in the 'file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,778,755 De Wolf Oct. 21, 1930684,152 Wheildon Oct. 8, 1901 2,403,976 Harvey- July 16, 194s 2,071,38()Bailey et al. Feb. 23, 1937 FOREIGN PATENTS Number Country Date 547,500France Sept. 23, 1922 362,491 Great Britain Dec. 2, 1931 154,112 GermanyAug. 6, 1904

